Electronic mail (email) use has become an integral part of people's daily lives. Many forms of communication, personal or business, have been replaced by email exchanges. Emails not only contain textual exchanges, but many modern email systems enable integration of multi-modal communications with emails. Thus, increasing amounts of textual, audio, video, and other forms of communication data is stored in individual mailboxes and central data storage facilities as part of the vast email exchange networks.
One characteristic of modern email systems is their diversity. Email systems may range from small email services set up by individuals to very large organizational email systems. As these diverse and numerous systems interact, security, privacy, and reliability are some of the aspects that have to be taken into consideration. For example, many email systems employ mailbox replication to protect against data loss.
Mailbox data replication across authentication boundaries like directory service systems (e.g. Active Directory® Forests) requires explicit credentials to be specified for data access across the authentication boundary. Relying on explicit credentials has challenges such as the credential having to be securely stored on the side that is driving the data replication, allowing another environment to store one of its credentials posing a risk to the side that is being accessed using this credential, and credentials expiring—hence they need to be managed separately in the remote forest for the data replication to continue—.